Field of the Invention
The present invention relates to a method for operating a magnetic resonance apparatus in order to implement an accelerated progression of a repeating pulse sequence with an optimized gradient curve. The invention also concerns a magnetic resonance apparatus operated according to such a method.
Description of the Prior Art
For a magnetic resonance examination, the body of a patient is typically exposed to a high basic magnetic field produced by a basic magnetic field system of a magnetic resonance apparatus. For the magnetic resonance examination, a magnetic field gradient is additionally applied by a gradient system of the magnetic resonance apparatus. The magnetic resonance apparatus has a radio-frequency transmission system for an emission of excitation signals (radio-frequency pulses). By means of the excitation signals (radio-frequency pulses), nuclear spins of atoms excited to resonance are deflected (flipped) by a defined flip angle relative to the magnetic field lines of the basic magnetic field. Upon a subsequent relaxation of the nuclear spins, radio-frequency signals (known as magnetic resonance signals) are radiated that are received by suitable reception antennas. The desired image data are subsequently reconstructed from the acquired magnetic resonance signals.
For a magnetic resonance measurement, a magnetic resonance sequence is emitted that is composed of a chronological series of radio-frequency (RF) pulses and gradient pulses emitted in coordination with the RF pulses, such as for slice selection and readout. The gradient pulses of the pulse sequence are defined by their gradient amplitude, gradient pulse duration and an edge steepness, or by the first derivative dG/dt of a pulse shape of the gradient pulses (also typically designated as a “slew rate”). An additional important gradient pulse value is the gradient pulse moment, which is defined as the integral of the gradient amplitude over time. It is a problem that the generation of eddy currents in conductive components of the apparatus increases with increasing gradient amplitudes and/or slew rates, and these eddy currents contribute to the generation of Lorentz forces that acoustic noise exposure also increases.
In order to minimize noise exposure, the gradient pulses are optimized with regard to their gradient curve. An optimized gradient curve is calculated for every single gradient pulse, which is very time-consuming.